Vibrational spectra and theoretical calculations of p-chlorophenol in the electronically excited S1 and ionic ground D0 states

With the good mass resolution (m/Δm) of about 650, the 35Cl and 37Cl isotopomers of p-chlorophenol have been separated successfully in our home made time of flight mass spectrometer (TOF-MS). One-color (1C), two-color (2C), resonant two-photon ionization (R2PI), and mass analyzed threshold ionization (MATI) spectra of the both isotopomers have been further recorded. Within the detection limit of our experiment, the band origins of the S1 ← S0 transition and the adiabatic ionization energies (IE) of 35Cl and 37Cl p-chlorophenol are measured to be the same. The band origins of the two isotopic species are determined to be 34813 ± 2 cm−1 by the 1C-R2PI experiment, and the adiabatic IE values are given to be 68094 ± 15 and 68104 ± 5 cm−1 by the 2C-R2PI and MATI methods for the two isotopomers of 35Cl and 37Cl p-chlorophenol. Analysis on the S1 ← S0 transition energy of para substituted phenols suggests that the band origins are all red shifted from phenol regardless of the nature of the substituent, while the inductive effect plays an important role for the D0 ← S1 transition process. The spectral properties of the two isotopomers in the electronically excited S1 and ionic ground D0 states are similar, whereas the vibrational frequencies of some modes are slightly different by a few wavenumbers, displaying the isotope effect.